This review describes version with OPA209, but other ones should perform on par or better and probably without GSM noise issue.
The amplifier is powerful enough to drive power hungry headphones such as orthodynamics, but also has very low impedance for balanced armature IEMs.
 
DAC, while very good, is not the absolute benchmark - but that is to be expected in an integrated device. Opamps can be replaced - they're SO-8 mono versions attached via a DIP-8 adapter.
The only actual drawbacks of this amp are related to ergonomics. Especially the very sensitive potentiometer can be problematic.

SE-5 is a true marvel of engineering, one of a few headphones/IEMs I can say brought a new level of detail and presentation to music and is truly high-fidelity, that is directly comparable to live performance given a high quality recording.
 
Important caveat: many amplifiers and sources (even many dedicated headphone amps) cannot drive SE-5 correctly - very low output impedance is required.
As a workaround, an impedance adapter can be used to reduce the impact of this on sound.
 
When improperly driven, they sound dull and dark due to exaggerated cut around 5-8kHz, unevenness above and lowpass. They're relatively dark in the highest registers anyway, which is the reason for 0.5 mark off the sound; but they're no darker than most dynamic driver IEMs.
 
(No, you don't really need a Benchmark DAC1 for them - FiiO E7 will do.)
 
Also, I had to wait about 4 months for them to be made, then had to get a refit, taking another month.
Of course the price is very high even for custom IEM standards, however you do get unparralelled quality for it, especially in lower registers.

Review is in the review thread here: http://www.head-fi.org/t/568515/hifiman-re272-review/135#post_7845383
 
Suffice it to say, these IEMs are perfect once equalized. No ifs or buts. Nothing I've ever tried matches these.
 
Even without the sound is great, if a bit bass lean and slightly forward.
Extension is unmatched by any other IEM.
 
I'd love if the next revision includes a case/pouch (not just jewel case) and inverse channel balanced cable.
Hifiman should really provide different tips - the included ones are unusable except the smaller biflange.
 
The included eartips are atrocious. Single flanges don't seal appreciably, large biflange is far too large, small biflange causes unpleasant bass texturing (kills impact) and glassy sound.
The good choices are in order of preference: Sennheiser small olives, VSonic single flange, Sony Hybrid tips (both M and S size)

See:
http://www.head-fi.org/t/564273/the-beyerdynamic-tesla-dt-1350-fan-club/75#post_7792890

This is an old highest end model of entry level headphone line by Sennheiser model, now replaced by the likes of HD 495.
Decent headphone for rock and trance. Lacks subbass and has grainy timbre. Definitely not what I'd call neutral, but it keeps the bass/mid/high balance decently for entry level.
Extension is ok for an entry level pair.
Cable tends to break by all three jacks - however is easy to replace, though the headphone side jacks are rare 2,5mm mono ones.
 
HD 497 leak a lot of sound and provide very little isolation, so are completely unsuitable for portable usage.
Comfort is okayish, though they can get a bit sweaty after very long usage.
Small circumaural fit is not for everyone. Headband is only adjustable in pretty large steps.
On the plus side for build quality, the plastic used is pretty much indestructible.

Beyerdynamics DT231 are an entry level model of the well known company.
These headphones are supraaural and sport fake velour pads for comfortable, albeit warm, feel.
The pads are of course user-replaceable.
 
Bass is hugely lacking in quantity, while highs on the other hand are boosted in the sparkly 8kHz region resulting in high-slanted sound signature. Detailing and soundstaging are good.
Timbre is ok with exception of bass, where it's poor with little impact and texture.
Comfort can be bad if you happen to have large ears. After a while, the ears will get warm and sweat due to velour pads. The pads can also get worn and start to scrape.
 
There are far better entry level headphones nowadays. No need to bother with these.

Bass is slightly boosted with a bit of extra warmth thrown in, but nowhere near the amount present in IE8.
Mids sound a bit aggresive with some 3.5k boost.
Highs are present, though not exactly delicate. Some 6k hump exists. Extension is ok, but the highest lack volume.
In general, the response is bass oriented, which is easy to correct with an equalizer. Timbre is a bit fat on this one. Not smooth, but a kind of "substantial", heavy-handed sound with not a lot of microdetail.
Comfort is excellent.
Isolation is mediocre - the vented design and shallow fit take its toll.
A decent set of tips is included in the package - single flange, biflange of 3 sizes and smallish olives. Cable is perfect, thick, tangle free and supple, with high quality straight 3.5mm jack, zero microphonics. Both ends are well strain-relieved.
Soundstage is huge and pretty far away, but intimacy is correctly rendered. Positioning precision could be better.
 
If not for the heavy handed detailing, these could be called an older brother of VSonic GR07. Sound signature is similar, with more bass emphasis and definitely no sibilance in the Sennheisers, but some slight veil.

These IEMs sport harsh sound, chubby build uncomfortable for smaller ears or ear canals. Due to chubby housings, I couldn't wear them for longer than few hours at a time.
 
Bass is pretty much lacking, as typical of balanced armature. It simply isn't there. What is there, lacks decay and impact completely.
Mids are good quality and quantity.
Highs are boosted in 8k region giving them a harsh, sometimes sparkly signature. Extension is not great, ending at 16kHz.
Detailing is exaggerated which combined with the sound signature sounds plain bad.
Soundstaging is of decent width, but a bit too close, decent resolution.
Cable hardens after contact with skin oils or heat. Plug is straight 3.5mm jack.

VSonic GR07 is a great example of IEM strong because it has few flaws and almost all of these are possible to correct with a good equalizer.
Bass is perfectly controlled, excellent texture, very well extended (-6 dB at 30 Hz with perfect seal), perhaps a bit warm due to high-bass boost (~250 Hz). No bass bleed is present.
Mids can be slightly forward to slightly laid back depending on tips and depth of fit.
Highs... here's the issue. With shallow insertion, there can be a fair amount of lower highs boost, around 6kHz, which combined with some highest end peaks can sound sibilant. Using foam tips helps with this, deep insertion completely removes this issue. GR07 don't have a lot of energy at the highest end, but they do have extension, so it can be corrected.
Timbre is excellent - delicate and unassuming, with excellent detailing, not overly aggresive and not overly smooth.
Soundstaging depends on depth of fit. With shallow fit, the soundstage isn't the widest, but is quite competent - with minor positioning issues due to sibilance and high-bass boost. With deep fit it is perfect, both width and depth, there's vertical resolution too - it will unfortunately make all recording and mixing flaws in this regard obvious.
Fit is excellent both for deep and shallow insertion due to rounded edges and no molding artifacts, small enough size and adjustable nozzle angle as well as a fairly large tip selection. GR07's nozzle is unusual sized though which limits possibilities. For Comply foams, T140 is the correct size.
Isolation is good for dynamic driver IEMs, microphonics are nonexistent.
Cable doesn't tolerate any kind of rotation around the axis of the cable for the part above Y split. If any is present, the cable tends to jump off the ear. This is easily remedied with the included ear guides or neck cable adjuster.
3.5mm L-shaped jack is iPhone friendly and seems very sturdy.
Build quality is very good with a minor exception - the strain reliefs tend to come apart from the body of the IEM. Easy to fix with a dot or two of superglue.
GR07 are efficient enough to be driven directly from a portable, do not gain a lot of quality when amplified.
 
Their main problem is availability - there are few sellers and those can be a bit remote.
 
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Now that my RE272 cable broke, I'm stuck with these. They need somewhat extreme equalization to get rid of the presence boost, but with T200 Small, truly a winner.
Of course they're somewhat less analytical, slightly lowpassed (17.5kHz) but beautiful texture.
Without eq they are pretty harsh and "flat" sounding, as in no depth, likely due to presence boost.
Equalization lets them have great depth resolution too.
 
GR07 bass sure is fast and tight, but it has less natural decay than RE272's. Kind of like it's trimmed or slightly compressed. However, vocals are presented far more liquid and with better detailing, while higher end (presence) sounds a bit electric/harsh even after correction.

These are budget-minded basshead's dream come true. Others might not be satisfied by the bottom-slanted sound, which can be hugely improved with equalization, otherwise they sound dark and laid back. The sound is precise, with engaging musical quality to it. Bass is very well controlled despite the amount. Mids are neither forward nor laid back, perhaps slightly boosted in upper registers. Highs are actually well extended, but overshadowed by the huge bass.
Brainwavz M2 are very efficient and despite it, don't hiss at all. However, they will pick all stray mains hum.